I believe the nicads in my Tek 1502-B TDR have failed. A few times, the unit operated for a limited time- 60 then 15 minutes, now, after a long charge, nothing. Can someone suggest low-cost method of replacing the batteries other than ordering from Tek? Can individual nicads be purchased, the ends soldered together and put in the battery box? Thanks, Jay (Please disregard the date-time error)